In a flash memory, the basic storage unit is a cell. Unlike traditional memories that only have a layer of gate oxide, the flash memory adds a floating gate between a gate and a channel in a metal oxide semiconductor (MOS), such that the flash memory can have three operating modes: write, read and erase. If an electron is added to the floating gate, the value of 0 will overwrite the value of 1 for the basic bit; and if an electron is removed, then the basic bit will be changed from 0 to 1, which is equivalent to erasing the memory.
The technology for executing a flash memory can be divided into single level cell (SLC) and multi level cell (MLC), and the MLC flash memory has a memory density twice as large as that of the SLC flash memory, and thus the MLC flash memory has a capacity higher than the SLC flash memory and gives the advantage of lighter, thinner, shorter and smaller features, and lower the cost per megabyte.
However, the electric charge and discharge properties of the flash memory physically restrict the number of times for writing and reading data, and each cell of the MLC flash memory only allows 10000 times of writing and reading data repeatedly, and each cell of the SLC flash memory can offer 100000 times of writing and reading data repeatedly. The high-capacity MLC flash memory only provides 10000 times for writing and reading data, and thus the cell will exceed its maximum number of writing and reading data and will be labeled as a bad sector. The life of the flash memory is reduced by the increase of bad sectors, and thus a method for recycling or rearranging the bad sectors in a flash memory is needed to extend the life expectancy of the flash memory.